Dolmar 64xx/73xx/79xx series, smurfs and solo 665/675/681 thread

[tickbitintn]

385 will probably stick around, it is NOT stock...

Was my brothers saw that originally came out of B.C.
Had some numbers carved in it... was a B.C. parks or hydro saw at some point.

It's the saw that got me started down this slippery slope!!

It's had a complete rebuild up from bare cases and lots of time and effort into it on top of all it's miles traveled.

Sent from my XT1635-01 using Tapatalk

 

[huskihl]

Could be the way each carb was tuned or how well one or the other was matched to the individual saw. I could feel a difference in power with the HD, but always felt the saw ran fine with the zama too.

@huskyboy

Been thinking about this, as well as what you said about leaning out in a long cut. Here's my take on it.

Take 2 372oe's for an example. Unlimited coils. One has an HD12, the other is running a larger WJ. The WJ obviously has a bigger venturi, so it'll have the ability to allow the saw to run at a higher rpm, at least with no load. If you tuned both saws to...say... 14,000 rpm. The wj would be burbling more heavily because it could have been tuned to 15k with a similar amount of 4 stroking as the HD at 14k. After a long cut, the wj with the richer tune would return to idle quicker, where the HD may hunt for a few seconds while it cooled off.

Could have been the same thing you experienced with the zama vs hd

 

[huskyboy]

@huskyboy

Been thinking about this, as well as what you said about leaning out in a long cut. Here's my take on it.

Take 2 372oe's for an example. Unlimited coils. One has an HD12, the other is running a larger WJ. The WJ obviously has a bigger venturi, so it'll have the ability to allow the saw to run at a higher rpm, at least with no load. If you tuned both saws to...say... 14,000 rpm. The wj would be burbling more heavily because it could have been tuned to 15k with a similar amount of 4 stroking as the HD at 14k. After a long cut, the wj with the richer tune would return to idle quicker, where the HD may hunt for a few seconds while it cooled off.

Could have been the same thing you experienced with the zama vs hd

A carb with a slightly smaller venturi could have the ability to be pulling more fuel because of the increased velocity. Now the other way around a carb with a big venturi and the same jetting as the smaller carb could be pulling less fuel needing more turns out on the jets. Example is a RWJ Xtorq carb. It has a huge venturi but it needs more turns out on the jets to deliver the same amount of fuel on the same saw than a way smaller venturi HD12 or even zama would. A wj71 off a 394 in comparison to the rwj flows way more fuel with close to same size venturi, because it’s got larger jetting. Less turns out on the jets than the rwj. Now I’m figuring the zama has smaller jetting than the HD6 (about same size venturi as a zama), or the hd12 (slightly bigger than the zama) because the walbro needs less turns out on the jets to deliver the same amount of fuel. It also doesn’t seem to lean out in long cuts as much tuned the same. I also noticed the same thing with a drilled zama vs a stock one on a ported 7910. Now if it was tried on a stock saw, it’s probably a waste of time. I could be wrong but this is just what I’m thinking.

 

[PA Dan]

A carb with a slightly smaller venturi could have the ability to be pulling more fuel because of the increased velocity. Now the other way around a carb with a big venturi and the same jetting as the smaller carb could be pulling less fuel needing more turns out on the jets. Example is a RWJ Xtorq carb. It has a huge venturi but it needs more turns out on the jets to deliver the same amount of fuel on the same saw than a way smaller venturi HD12 would. A wj71 off a 394 in comparison to the rwj flows way more fuel with close to same size venturi, because it’s got larger jetting. Less turns out on the jets than the rwj. Now I’m figuring the zama has smaller jetting than the HD6 (about same size venturi as a zama), or the hd12 (slightly bigger than the zama) because the walbro needs less turns out on the jets to deliver the same amount of fuel. It also doesn’t seem to lean out in long cuts as much tuned the same. I also noticed the same thing with a drilled zama vs a stock one on a ported 7910. Now if it was tried on a stock saw, it’s probably a waste of time. I could be wrong but this is just what I’m thinking.

Damn that's a lot of thinking!

 

[huskyboy]

Damn that's a lot of thinking!

Maybe I’m overthinking it. Lol

 

[PA Dan]

Maybe I’m overthinking it. Lol

I dont think so...there is something there so keep thinking!

 

[RI Chevy]

Bigger carbs generally have larger jets. Which, in turn flow more air and fuel...
So one shouldn't really have to open the H and L any more than normal.
Just my theory...

 

[chipper1]

385 will probably stick around, it is NOT stock...

Was my brothers saw that originally came out of B.C.
Had some numbers carved in it... was a B.C. parks or hydro saw at some point.

It's the saw that got me started down this slippery slope!!

It's had a complete rebuild up from bare cases and lots of time and effort into it on top of all it's miles traveled.

Sent from my XT1635-01 using Tapatalk

That's why I left that out lol.
Sounds like a great saw!

 

[huskihl]

Bigger carbs generally have larger jets. Which, in turn flow more air and fuel...
So one shouldn't really have to open the H and L any more than normal.
Just my theory...

Not necessarily true when fitting a large carb on a small saw. The larger intake tract slows down the airflow and pulls less on the high speed nozzle

A wj-6 from an 064 won't allow enough fuel on dall's piped 026.

 

[Canadian farm boy]

Bigger definitely ain’t always better especially when it comes to the intake track. Velocity plays a big part when it comes to fuel supply.

 

[Wood Chopper]

Bigger definitely ain’t always better

Phew!!

 

[RI Chevy]

Not necessarily true when fitting a large carb on a small saw. The larger intake tract slows down the airflow and pulls less on the high speed surface.

A wj-6 from an 064 won't allow enough fuel on dall's piped 026.

Then jet up!

 

[Deets066]

Then jet up!

I have a 74 jet in a WJ 69 on my 024 super.

It wouldn’t feed enough fuel, had to do a little work to the Venturi to get it to pull more from the H jet

 

[huskihl]

Then jet up!

I opened every hole in the high speed circuit from .7mm up to 1.3mm. Even the needle seat. The only thing left was the diameter of the needle itself not allowing fuel past it.

I just swapped to a wj69 with a main jet. Lots of fuel now

 

[Rob Stafari]

Paging @Terry Syd @Poleman These guys are getting into carb theory and I'm not smart enough like yous...

 

[huskyboy]

I opened every hole in the high speed circuit from .7mm up to 1.3mm. Even the needle seat. The only thing left was the diameter of the needle itself not allowing fuel past it.

I just swapped to a wj69 with a main jet. Lots of fuel now

So a wj69 is a superior/upgrade carb to say the earlier wj’s that came on 064/066?

 

[RI Chevy]

At least we have some good dialog going...

 

[dahmer]

At least we have some good dialog going...

Only if you understand Greek! I kinda have the caveman outlook. Saw start, saw cut wood, unghhh good!

 

[huskihl]

So a wj69 is a superior/upgrade carb to say the earlier wj’s that came on 064/066?

Idk about a superior upgrade. If your wj6 on your 064 puts out enough fuel for your 064, then it won't matter.

Wj69 has the ability to flow more fuel. But if the venturis are the same, and the 6 is fine, there's no sense in swapping to the 69.

Just because someone adds a bigger main jet doesn't mean their saw is gonna run stronger, it just means that the needle is gonna need to be turned in further

 

[huskyboy]

Idk about a superior upgrade. If your wj6 on your 064 puts out enough fuel for your 064, then it won't matter.

Wj69 has the ability to flow more fuel. But if the venturis are the same, and the 6 is fine, there's no sense in swapping to the 69.

Just because someone adds a bigger main jet doesn't mean their saw is gonna run stronger, it just means that the needle is gonna need to be turned in further

Thanks for the info. I have a wj41 if I’m not mistaken. Looked like it had 70 written on the jet in the carb when I rebuilt it. Not a removable type jet either. It can be a tad touchy tuning on the L, as in its easy to make it too fat on L. So it seems jetted rich. Seems to run ok. I know this is a dolmar thread... but it’s on topic because it’s we’re talking about carbs lol.